The invention relates to impact mechanisms, and more particularly to impact mechanisms operated with gaseous fluid under pressure, such as with compressed air or steam.
The present invention is preferably used in pneumatic impact mechanisms employed in the mining industry, such as deep-well pneumatic hammers, rock drills and pick hammers.
The invention may also be used in constructional equipment, for instance pneumatic pile drivers, air-operated moles for driving holes in soil and pavement breakers.
The invention may be used also for improving other types of impact mechanisms employed by engineering organizations, for instance in the construction of chipping and riveting hammers, tamping tools and the like.
At present, two types of impact mechanisms operated with gaseous fluid under pressure are known, namely those in which gaseous fluid is distributed into the chambers of the mechanism with or without the employment of a valve.
Known in the art is a valveless pneumatic impact mechanism comprising a hollow casing accommodating a reciprocating piston which divides the inner space of the casing into a work stroke chamber and an idle stroke chamber. There is a socket at one end of the casing for receiving a working implement, and at the other end, the casing is provided with a distribution chamber. The piston of the mechanism comprises a shank and a head, the shank facing the distribution chamber. For feeding gaseous fluid under pressure at regular intervals to the work stroke chamber and to the idle stroke chamber and for discharging exhaust gaseous fluid into atmosphere, the mechanism includes, means for distributing gaseous fluid comprising a counterbore of the casing in the zone of contact with the piston shank communicating with the distribution chamber; inner passage of the piston has one end opening to the idle stroke chamber and its other end opening to the periphery of the shank in the zone of contact thereof with the inner surface of the casing. There is also provided an outer passage on the piston shank disposed between the surface of the shank in contact with the casing and the piston head, and ports in the casing for discharging exhaust gaseous fluid.
When the distribution chamber of the casing is connected to a source of gaseous fluid under pressure, the fluid is admitted to the counterbore of the casing and proceeds therefrom, depending on the position of the piston relative to the casing, either to the idle stroke chamber, via the inner passage of the piston, or to the work stroke chamber, via the outer passage of the piston shank. Communication of the chambers of the mechanism with the source of gaseous fluid under pressure at regular intervals, via the above-mentioned passages, and with the atmosphere, via the ports of the casing, provides for reciprocations of the piston so that the piston delivers a blow to the working implement at the end of a work stroke.
The valveless pneumatic impact mechanism is characterized in that the beginning and the end of the admission of gaseous fluid to each chamber occurs at the same position of the piston relative to the casing. This results in a rapid deceleration of the piston during the idle stroke, lowers the pressure of gaseous fluid in the chambers of the mechanism and reduces impact energy and power.
Another known pneumatic impact mechanism includes a casing with the inner space accommodating a reciprocating piston dividing said inner space of the casing into a work stroke chamber and an idle stroke chamber. There is provided a socket at one end of the casing for receiving a working implement, and the other end of the casing is provided with a distribution unit including a distribution chamber and a valve box. The valve box accommodates a rigid plate valve mounted for limited reciprocations. When in the extreme position, the valve bears against one of annular projections provided on the opposite working surfaces of the distribution unit to define a valve aperture with the opposite annular projection. The annular projections and the valve divide the valve box into three portions: an outer portion, connected with the distribution chamber and two inner portions separated by the valve and one inner portion being connected with the work stroke chamber and the other inner portion being connected with the idle stroke chamber.
There are provided ports in the casing for discharging exhaust gaseous fluid from the chambers into the atmosphere.
When the distribution chamber of the distribution unit is connected to a source of gaseous fluid under pressure, the fluid is admitted, via the valve aperture, to the idle stroke chamber to enable or commence the idle stroke of the piston. The valve aperture defined by the annular projection and the valve on the opposite side of the valve is closed by the valve at this moment so that gaseous fluid is not admitted to the work stroke chamber. When the piston leaves open the ports of the casing connecting the idle stroke chamber with the atmosphere, the pressure of gaseous fluid in the chamber and at the valve surface located inwardly of the open valve aperture decreases. The pressure of gas at the opposite side of the valve mounted inside the closed valve aperture increases due to the compression of gas in the work stroke chamber. During further movement of the piston, the resultant force applied to the valve changes its direction to cause the displacement of the valve. The valve aperture, which connected the idle stroke chamber to the distribution chamber beforehand, is closed, and the opposite valve aperture provides for the admission to the work stroke chamber is opened. The work stroke chamber is filled with gaseous fluid under pressure. The piston is stopped and then performs the work stroke. At the end of the work stroke, the piston leaves open the port of the casing to connect the work stroke chamber with the atmosphere. The pressure of gaseous fluid in the work stroke chamber decreases, and the pressure of gas in the idle stroke chamber increases due to compression of the gas by the piston.
This causes the displacement of the valve to open the valve aperture controlling the admission of gaseous fluid to the idle stroke chamber and to close the opposite valve aperture. After a blow is imparted by the piston to the working implement, the above-described cycle is repeated.
The main disadvantage of the valve-type pneumatic impact mechanism resides in that a substantial pressure drop is required to displace the valve in the chamber which was filled through the valve prior to the displacement thereof. A delay in the displacement of the valve relative to the moment of the beginning of opening of the exhaust ports of the casing by the piston results in an increase in consumption of gaseous fluid under pressure. The live section of the valve apertures in such mechanism is relatively small thus resulting in reduced average pressure in the chamber and lower power. The attempts to increase the live section of the valve apertures result in significant increase in the consumption of gaseous fluid under pressure and unstable performance of the mechanism.
The attempts to reduce the consumption of gaseous fluid under pressure has resulted in the provision of valve-type pneumatic impact mechanisms in which a rocking plate valve is used. Such impact mechanism are provided with a valve having the form of an elongate rhombic mounted with the obtuse angle thereof to the working surface of the distribution unit and defining therewith apertures which are wedge-shaped at lateral sides. Two passages of the distribution unit open to the working surface thereof on either side of the line of contact of the valve and the distribution unit, one passage being connected to the work stroke chamber and the other passage, being connected to the idle stroke chamber. Upon rocking of the valve about the line of contact with the distribution unit, one passage of the working surface thereof is opened by the valve, and the other passage is concurrently closed by the valve, and vice versa.
The pneumatic impact mechanism with rocking valve functions in the same manner as that with the plate valve the above-described mechanism.
The main disadvantage of the pneumatic impact mechanisms incorporating a rocking valve resides in a small live section of the valve apertures which does not enable high average pressure in the chambers of the impact mechanism, lowers the impact energy and power.
It is also known to use, in pneumatic impact mechanisms, combined means for distributing gaseous fluid to admit the fluid to the chambers of the mechanism through the casing passages and piston passages when the latter are brought in register with the casing passages, and additionally to admit gaseous fluid to the chambers via a valve.
Also well known is a pneumatic impact mechanism including a casing accommodating a reciprocating piston having a head and a hammer rod, the piston dividing the inner space of the casing into a work stroke chamber and an idle stroke chamber. A socket is provided at one end of the casing to receive a working implement, and a valve-type distribution assembly is provided at the other end of the casing. The piston is mounted with the hammer rod thereof facing the working implement, and a groove is made in the periphery of the piston. The casing has radial passages and ports, the passages communicating with the distribution chamber and opening to the inner periphery of the casing, and the ports connecting the inner space of the casing with the atmosphere. The piston of the mechanism is provided with a central passage. The valve-type distribution assembly of the mechanism comprises a distribution unit and a valve made in the form of a cantilevered flexible plate which is mounted in a spaced relationship with ports of the distribution unit opening, at the opposite end, to the work stroke chamber. The valve space defined by the distribution unit, valve and casing is connected with the distribution chamber.
When the distribution chamber is connected to a source of gaseous fluid under pressure, the fluid is exhausted into the atmosphere, via the gap between the valve and distribution unit, the ports of the distribution unit, the work stroke chamber and the ports of the casing. Under the action of pressure difference of gaseous fluid between the valve space and the idle stroke chamber, the valve is deflected to close the ports of the distribution unit and to seal the work stroke chamber off from the distribution chamber. At the same time, fluid under pressure is admitted via the radial passages of the casing and groove of the hammer rod of the piston, to the idle stroke chamber to enable or commence the idle stroke of the piston.
When the hammer rod of the piston closes the radial passages of the casing, the admission of gaseous fluid under pressure to the idle stroke chamber is interrupted, and fluid is then discharged from this chamber upon opening of the casing ports by the piston head. During this time, the hammer rod of the piston opens the radial passages of the casing to admit gaseous fluid under pressure to the work stroke chamber, via the central passage of the piston. The pressure difference of gaseous fluid at the valve decreases, and the valve is straightened under the action of elastic forces to open the ports of the distribution unit so as to admit gaseous fluid from the distribution chamber to the work stroke chamber. The piston is stopped and then performs the work stroke.
During the work stroke of the piston, the work stroke chamber, at the initial period of piston movement is connected with a source of gaseous fluid under pressure via the valve and concurrently, via the radial passages of the casing.
When the hammer rod of the piston closes the radial passages of the casing, gaseous fluid under pressure is only admitted to the work stroke chamber through the valve. Further, the piston leaves open the casing ports, and the fluid is discharged from the work stroke chamber. The pressure in the work stroke chamber decreases, and the pressure difference acting on the valve increases. With a predetermined pressure difference value, the value is deflected to close the ports of the distribution unit. At this moment, the groove of the hammer rod of the piston is brought in register with the radial passages of the casing to provide for admission to the idle stroke chamber. After the delivery of a blow to the working implement, the piston performs the idle stroke.
The pneumatic impact mechanism having combined distribution means features a low specific consumption of gaseous fluid under pressure. The main disadvantage of this mechanism resides in a small live section of the valve and relatively large size of the distribution assembly hampering the incorporation of the mechanism in small-diameter casings.
It is known that power, consumption of gaseous fluid under pressure, simplicity, mass and size of the mechanism are the main factors influencing the performance and efficiency of impact mechanisms operated with gaseous fluid under pressure.
The level of quality of impact mechanisms mainly depends on design, function and consumption characteristics of means for distributing gaseous fluid under pressure to the chambers of the mechanism for enabling reciprocatory movement. Small live section of passages for admission of gaseous fluid to the chambers of the mechanism, complicated structure and large size are among the main disadvantages of the existing distribution means.